This paper discusses the thermal effect of covering the building envelope with vegetation on the microclimate in the built environment,
for various climates and urban canyon geometries. A two-dimensional, prognostic, micro scale model has been used, developed for the
purposes of this study. The climatic characteristics of nine cities, three urban canyon geometries, two canyon orientations and two wind
directions are examined. The thermal effect of green roofs and green walls on the built environment is examined in both inside the canyon
and at roof level. The effects of this temperature decrease on outdoors thermal comfort and energy savings are examined. Conclusions
are drawn on whether plants on the building envelope can be used to tackle the heat island effect, depending on all these parameters
taken into consideration.